do not rename variables declared in second and subsequent

Created by: tuchida

example:

var a = 10;
var b = 20;
macro main {
  case () => {
    (function() {
      var a = 100, b = 200;
      return sub();
    })();
  }
}
macro sub {
  case () => {
    a + b
  }
}

var z = main();

expect(z).to.be(30);

I expected 30. But returned 210. b = 200 was not renamed.